The invention relates to a compressed gas weapon having a barrel and a stock. A portion of the barrel distant from the muzzle is configured to receive a projectile in a position of readiness to fire and to caliber the projectile when conveyed into the position of readiness to fire. Conventionally, the ammunition for compressed gas weapons, as seen in a direction perpendicular to the axis of the barrel has a maximum outside diameter that is slightly oversized relative to the bore of the barrel. This excess must be reduced upon introduction of a projectile into the barrel: the projectile is calibered when it is introduced into the barrel. This is intended to ensure that the projectile, in its position of readiness to fire, will obturate the bore in the direction towards the muzzle, so that upon firing, the full gas pressure will contribute to accelerating the projectile, and no portion of the gas will be able to escape past the projectile.
In compressed gas weapons of this kind, it has been found that the location of the impact of the projectile at the target depends critically on the manner in which the projectile was introduced into the barrel. Thus for example different marksmen will obtain different firing patterns, even if the weapon has been trained on the target and clamped down firmly, the trigger is pulled automatically, and only the introduction of the ammunition is done manually. Even the same individual marksman will obtain different patterns depending on whether he places the ammunition in the barrel carefully or carelessly. Users find this situation highly unacceptable.